Inspection device and inspection method for boiler furnace water wall tubes

An inspection device and an inspection method for boiler furnace water wall tubes. The inspection device includes a scanner including columns placed upright and fixed by magnets onto the surfaces of multiple water wall tubes extending in the up-down direction on the inner wall surfaces of the boiler furnace, a support frame fixed to the columns to support a displacement sensor producing laser light to be irradiated onto the surface of a water wall tube, and a moving mechanism for moving the displacement sensor in the axial direction of the water wall tube relative to the support frame. A signal processing unit calculates the amount of reduced wall thickness of the water wall tube from a difference between the cross-sectional surface shape of the water wall tube based on a signal from the displacement sensor and a reference shape without reduction in wall thickness.